1. Field of the Invention
The present invention relates to a method and apparatus for manufacturing a semiconductor device, and more particularly to a manufacturing method capable of reducing generation of a resin piece, a press die and a guide rail.
2. Description of the Background Art
In general, a semiconductor device has a structure in which an integrated circuit portion (a semiconductor chip) is sealed with an insulating material such as a resin, and includes a lead extending through the insulating material for electrical connection of an integrated circuit to an external portion. In the following description, a quad flat package (QFP) will be taken as an example.
First of all, a process of manufacturing the QFP will be described below. In general, a flat package semiconductor device such as the QFP is formed by mounting a semiconductor chip on a terminal member referred to as a lead frame and sealing the semiconductor chip with a resin.
The semiconductor chip is first fixed (die bonded) to a portion referred to as a die pad of a lead frame 20 and is connected (wire bonded) to a lead by wiring. Then, the semiconductor chip is sealed with a sealing resin 3. The lead frame 20 is band-shaped and has a structure in which a plurality of semiconductor chips are arranged.
FIG. 30 is a plan view showing the lead frame 20 in a state in which the semiconductor chip is completely sealed with the resin. In FIG. 30, a plurality of sealing resins 3 are arranged in a line. At a resin sealing step, the semiconductor chip is enclosed by a die to form a cavity, and a liquid resin is poured into the cavity. Then, the resin is cured to form the sealing resin 3. A path (gate) for introducing the resin remains on a surface of the lead frame 20 with the resin filled therein. When the lead frame 20 is separated from the die, most of the gate is removed (gate break). A residual portion of the gate makes a remaining gate 3a.
As shown in FIG. 31, the lead frame 20 is divided by press molding for each section corresponding to one semiconductor device (single substance cut). At this step, a divided lead frame 2 is obtained. In this stage, the lead frame 2 has a tie bar TB in a lead LD.
Then, the tie bar TB is removed by the press molding as shown in FIG. 32 (tie bar cut).
Thereafter, four corners of the lead frame 2 are removed by press molding as shown in FIG. 33 (pinch cut). At a pinch cut step, the four corners of the lead frame 2 are connected to a die pad (not shown) on which the semiconductor chip is mounted and a pinch portion (not shown) of a suspension lead supporting a die is cut away. At this time, the remaining gate 3a is also removed. At this step, the lead frame 2 remains on only a tip of a lead group LG extending from the sealing resin 3 in four directions.
Subsequently, an unnecessary portion of the lead frame 2 remaining on the tip of the lead group LG is removed and the lead LD is subjected to bending. Thus, the QFP is finished.
Since the semiconductor device according to the prior art has been manufactured by the above-mentioned method, it has had the following problems.
FIG. 34 is a detailed diagram showing a structure in FIG. 32. As shown in FIG. 34, a pinch portion 2b of the suspension lead extends from four corners of the sealing resin 3, and is connected to four corners 2a of the lead frame 2. At the pinch cut step, the four corners 2a of the lead frame 2 are removed. In this case, the remaining gate 3a becomes a problem. The remaining gate 3a extends from the corner of the sealing resin 3 to a surface of the corner 2a of the lead frame 2.
FIG. 35 is a perspective view showing an X region in FIG. 34. At the pinch cut step, the lead frame 2 is cut away along the virtual cutting line CL shown by a broken line in FIG. 35 so that the corner 2a is removed. In this case, the pinch portion 2b is torn for removal.
The remaining gate 3a is a residual portion of the gate formed by an upper gate method. In the case where the gate is formed by a lower gate method, a remaining gate is formed in a position which is vertically reverse to that of the remaining gate 3a. The same remaining gate is indicated at 3b. FIG. 36 corresponds to FIG. 35 in which the remaining gate 3b is formed.
A step of removing the remaining gate 3b shown in FIG. 36 will be described below with reference to FIGS. 37 and 38. As shown in FIG. 37, the lead frame 2 is mounted on a die 9. FIG. 37 is a sectional view showing the corner 2a. A punch 8 descends from above the corner 2a. The punch 8 presses down the corner 2a so that a cutting line CL portion which is not shown is cut away and the pinch portion 2b is torn at the same time. At this time, the remaining gate 3b is broken off together with the corner 2a. In that case, a stress converges on a bottom portion of the remaining gate 3b so that the sealing resin 3 is broken off and a resin fracture portion 3d is formed or a crack is generated. When the remaining gate 3b is broken off, a resin piece is sometimes generated.
In the process of manufacturing a semiconductor device which has been described with reference to FIGS. 30 to 33, the lead frame 2 is often slid and carried on a guide rail. However, the remaining gate 3b exists on a lower face of the corner 2a of the lead frame 2, that is, on a face on a side which comes in contact with the guide rail as described above with reference to FIG. 36. As shown in FIG. 34, a remaining air vent 3e exists in each of the three corners of the sealing resin 3 except the corner where the remaining gate 3a (or the remaining gate 3b) is formed.
An air vent serves to prevent air accumulation from being generated in the cavity when the liquid resin is poured from the gate into the cavity, and is provided on each of three corners of the cavity. Accordingly, the resin is filled in so that it overflows from the air vent. The overflowing resin is cured so that the remaining air vent 3e is formed. The remaining air vent 3e is formed on upper and lower faces of the lead frame 2.
Consequently, the remaining gate 3b and the remaining air vent 3e rub against the guide rail when the lead frame 2 is slid on the guide rail. At this time, there is a possibility that a resin piece might be generated from the remaining gate 3b and the remaining air vent 3e and might cut into the sealing resin 3 or stick to the surface of the lead LD.
In the process of manufacturing a semiconductor device which has been described with reference to FIGS. 30 to 33, the press molding is performed. During the press molding, the remaining gates 3a and 3b and the remaining air vent 3e might be crushed to generate the resin piece. For example, if a processing proceeds to another press step in a state in which the resin piece adheres to the sealing resin 3 or the lead LD, the resin piece might cut into the sealing resin 3 or stick to the lead LD at the same press step.
Thus, the method for manufacturing a semiconductor device according to the prior art has had a problem that the sealing resin is damaged and the resin piece cuts into the sealing resin and sticks to the lead, thereby causing product failures.